It is known that in the field of continuous casting it is provided to discharge molten metal into a mold, also called crystallizer, to at least partly solidify the liquid metal and confer on it a predefined shape. Examples of continuous casting apparatuses having a curved casting line are described in documents GB-A-2.105.229, US-A-2014/090792, DE-A-10.2006.005635, EP-A-2.441.540, and US-A-2004/020632.
With reference to FIGS. 1 and 2, a casting apparatus according to the state of the art is shown, in which the crystallizer 111, for casting billets or blooms, is defined by a tubular body 112, in which the liquid metal M cools. It is also known to provide that the tubular body 112 is provided, in the thickness of its walls, and for at least part of the longitudinal development, with a plurality of cooling channels 117 through which a cooling liquid flows, which indirectly subtracts heat from the liquid product by means of the heat exchange that occurs between it and the walls in contact with the coolant.
The cooling inside the crystallizer is called primary cooling.
By means of the heat exchange, the product P starts to solidify externally, determining the formation of a surface skin 113 that becomes thicker as the product P approaches the exit from the crystallizer 111. The formation of the thickness of the skin 113 is influenced by the casting speed and therefore by productivity. The casting speed determines the permanence of the skin 113 in the crystallizer 111.
Normally, in this type of continuous casting apparatus, it is necessary to support the product P at exit from the crystallizer 111, due to the problems described below.
The external surfaces of the metal product are normally supported, along the casting line, by special roller guide systems, or mobile containing sectors 114, substantially parallel to the faces of the product P which they have to support.
Each containing sector 114, as shown in FIG. 2, is normally provided with a plurality of rollers 116 located so as to laterally surround the lateral section of the product P which is cast, so as to define the containment of the latter.
At the same time, the thickness of the skin 113 in formation must also be increased by means of a direct cooling of the product P, called secondary cooling.
The secondary cooling can take place either by means of said mobile sectors 114, provided with an internal cooling system, or by means of sprays 115, using normal or nebulized water, accompanying the product P until the inside is completely solidified in the so-called kissing point K, that is, the point along the casting line where the cross section of the cast product P is completely solidified.
The containing sectors 114 therefore constitute the external skeleton which allows the product P to descend along the casting line, to cool down and to pass from a vertical position to a horizontal position, following the theoretical casting radius of curvature.
The containing sectors 114, moreover, accompany the cast product P toward the straightening units which draw the cast product P out of the casting apparatus.
Along the casting line, in a zone comprised between the containing sectors 114 and the straightening units, there are normally support and bending rollers 118 provided to support and curve the metallic product P from the vertical condition to the horizontal condition. The support and bending rollers 118 are located distanced along the casting line and alternately one on the intrados side and the next on the extrados side of the casting line.
As we said, the mobile containing sectors 114 are necessary not only to cool the product P, but also to support the faces defining the product itself. In fact, the skins forming the product P are characterized by having a rather low thickness, and are subject to the phenomenon of “bulging”, that is, a swelling effect caused by the ferrostatic pressure which thrusts toward the outside the fraction of liquid product, swelling the walls of solidified skin.
Normally this phenomenon is contained by the containing sectors 114, which limit the entity thereof to negligible bulging, and which therefore do not compromise the castability of the product P.
In fact, if these swellings were free to manifest themselves, the skin 113 in formation of the product P would be subject to breakages. These breakages can be localized on the surface, causing a reduction in the quality of the product P cast, or they can determine a complete rupture of the skin with the consequent leakage of liquid metal (break out). In addition to constituting a danger, this determines very high maintenance and considerable economic losses.
However, even with the use of the mobile containing sectors 114 the casting process is not risk free.
In fact, it is essential to have a perfect alignment of the mobile containing sectors 114 with respect to the product P, both downstream of the crystallizer 111 and also along the rest of the casting line, until it engages with the straightening units downstream.
The alignment of the containing sectors 114, in fact, has to follow the natural shrinkage of the skin of the product P, which takes place as a consequence of cooling. If, for some reason, the contact between the skin and the containing sectors 114 were to occur in an inappropriate way, there are concrete possibilities that the skin can be pinched or torn, thus causing potential break-outs.
In any case, the maintenance made necessary by the containing sectors 114 is quite high, given that each face of the product P is supported by a containing sector 114 for almost the entire casting curve. Furthermore, the alignment must be done manually by operators outside the casting line, so great expertise is required during assembly in the work place, given that the containing sectors 114 often become misaligned during this step.
There is therefore a need to perfect a casting method which overcomes at least one of the disadvantages of the state of the art.
One purpose of the present invention is to perfect a continuous casting method which is efficient and allows to achieve high productivity.
It is also a purpose of the present invention to perfect a continuous casting method which allows to limit maintenance interventions on parts of the casting apparatus.
Another purpose of the present invention is to perfect a continuous casting method which allows to increase the quality of the cast products.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.